1. Technical Field
The present invention generally pertains to motor vehicles. More particular, the present invention pertains to a cooling fan system for a motor vehicle. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to a cooling fan system of a motor vehicle which incorporates a mechanical fan which rotates in a first direction and an electrical fan which rotates in a second, counter direction.
2. Discussion
Modern motor vehicles incorporate a fan, often referred to as an engine cooling fan or radiator fan, for cooling the engine. Such fans are typically engine driven. Engine cooling studies conducted on passenger cars and trucks have shown that operation of such engine cooling fans is required only a fraction of the time a vehicle is on the road. If the fan is run at a high speed when generally not required, additional fuel may be unnecessarily consumed and the noise produced may be objectionable. For these reasons, various arrangements have been heretofore developed to reduce the high speed operation of the mechanically driven fans as well as to control the operation in an effort to reduce the total energy required for operating the fan.
In one common type of arrangement, viscous couplings have been employed for engaging and disengaging the fan. These viscous couplings typically rely on the drive force created by fluid shear which occurs between two members having mating annular grooves and ridges or mating surfaces. The fan speed is dependent upon the speed of the driving element and the amount of working fluid in the mating grooves and ridges or between the operating surfaces. When the grooves are only partially filled, considerable slip occurs between the two members and the fan speed is considerably less than the speed of the driving member. When the space between the grooves and the ridges is completely filled with fluid, slip above a first predetermined engine speed would be reduced. When the speed of the driving element rise above a second predetermined value, the viscosity and shear characteristics are such that an increased amount of slippage occurs to prevent substantial increase in fan speed. Particular cooling fan arrangements incorporating viscous couplings are shown and described in commonly assigned U.S. Pat. Nos. 4,134,484 and 4,278,159. U.S. Pat. Nos. 4,134,484 and 4,278,159 are hereby incorporated by reference as if fully set forth herein.
To a more limited extent, it has been heretofore proposed to provide a cooling system for a motor vehicle which incorporates an electrical fan which is supplemented by a mechanical fan. For example, the cooling system of the 1996 Ford Crown Victoria includes an electrically driven fan driven by a single speed fan motor and a mechanically driven fan driven through a clutch. A temperature-controlled fluid coupling regulates the speed of the mechanically driven fan according to the temperature of air coming through the radiator core and flowing around a bi-metal control valve located on a forward face of the fan clutch.
While certain advantages may have been provided by prior art arrangements, including but not limited to those discussed above, they are all associated with disadvantages. For example, known cooling arrangements incorporating a mechanical fan driven through a clutch require a moderate to high engine speed for cooling fan disengagement. Typically, the disengage speed for an engine driven fan is approximately 1500 revolutions per minute (RPM) when the vehicle is operating at a road speed of 60 miles per hour (MPH). As the vehicle speed increases, the disengage speed for the engine driven fan increases in some proportional amount. The disengage speed for some engine driven fans can exceed 2800 engine RPM.
In such known arrangements, the moderate to high disengage speed is required to maintain the desired engine cooling temperatures and air conditioning compressor pressures. It is also a factor in enabling a linear modulating fan drive to perform properly. However, it is readily apparent to those skilled in the art that reduction in fan power requirements translates to vehicle fuel savings and horsepower gain.